The present invention relates to a tiltable steering column for an automotive vehicle, and more particularly relates to such a tiltable steering column for an automotive vehicle, which is suitable for being adjusted so as to conform the driving position to the particular physical build and preference of an individual driver, which is improved in terms of fittability and assemblability.
As an overall construction, a tiltable steering column for an automotive vehicle comprises a main steering shaft comprising a lower steering shaft and an upper steering shaft tiltably rotationally connected to said lower steering shaft, and a column tube assembly, comprising a lower tube which rotatably supports said lower steering shaft from the body of said automotive vehicle, and an upper tube which rotatably supports said upper steering shaft and is pivotally mounted so as to be able to tilt relative to said lower tube. Further, it is known for such a tiltable steering column for an automotive vehicle to comprise a tilt locking mechanism which comprises a ratchet mechanism comprising: a ratchet fixedly attached to one of said upper tube and said lower tube; a pawl pivotally attached to the other of said upper tube and said lower tube; a means for biasing said pawl so as to engage it with said ratchet, which acts constantly; and a means for selectively biasing said pawl so as to release its said engagement with said ratchet. Thereby, by operating the releasing means for the pawl, the engagement of the pawl to the ratchet is released, and the upper tube can be rotatably tilted with respect to the lower tube, thus enabling the position of the steering wheel, which is fixed to the upper end of the upper steering shaft, to be adjusted so as to conform the driving position to the particular physical build and preference of an individual driver.
According to such a tiltable type steering column, for instance the ones disclosed in Japanese Utility Model Publication Ser. No. 57-53730 (1982) and Japanese Utility Model Laying Open Publication Ser. No. 58-163354 (1983), neither of which is it intended to admit as prior art to the present application except to the extent otherwise required by law, the upper tube is rotationally locked with respect to the lower tube and thus the vehicle body by the tilt locking mechanism; but, since the tilt locking mechanism is in principle provided only on one side of the steering column assembly, the lateral support rigidity for the upper tube is not always sufficient, and good vibrational characteristics cannot be assured in all cases. And, in the worst case, sideways skewing of the steering wheel could in principle occur.
In view of these problems, the present applicant, in Japanese Utility Model Application Ser. No. 59-106772, which again it is not intended hereby to admit as prior art to the present application except to the extent otherwise required by law, has proposed a tiltable steering column in which two such tilt locking mechanisms are located one on each side of the steering column; and the two release levers of these two tilt locking mechanisms are synchronized by way of a connecting shaft. Further, attention is drawn to U.S. patent applications Ser. Nos. 811,289 and 870,740 which, again, it is not intended hereby to admit as prior art to the present application except to the extent otherwise required by law.
As a result of this arrangement, in such a tilt steering device, since the upper tube of the steering column is supported by a pair of tilt locking mechanisms arranged on both sides of the steering column, the lateral rigidity of the support of the upper tube can be increased, and good vibrational characteristics can be obtained, with the additional advantage that, since the release levers of the two tilt locking mechanisms are synchronized, the rotational operation of only one of the release levers is required for releasing the locking action of the two tilt locking mechanisms, and accordingly the operability of the device is quite good.
The problem however arises that, since the two sides of the upper and lower tubes are individually locked together by the two tilt locking mechanisms, the accuracy of fitting of these mechanisms is crucial. Specifically, a slight difference in the phases of the teeth of the two ratchets, or other divergence from the ideal due to manufacturing variations of the parts, can prevent the proper engagement of one of the two tilt locking mechanisms, and it is extremely difficult to properly ensure simultaneous meshing of the two pawls with the two ratchets, because of the inevitability of dimensional variations of the parts during manufacture, as well as because of the inevitability of assembly variations of the steering column structure.